496 Ton Meteorite

While searching the internet i can across this

June 24, 1938 – A 450-metric-ton (496-short-ton) meteorite explodes about 12 miles (19 km) above the earth near Chicora, Pennsylvania

en.wikipedia.org...

On June 24, 1938 a meteorite fell in the vicinity of Chicora. Named the "Chicora Meteor", the 450+ tonne meteorite exploded approximately twelve miles above the Earth's surface. Only two fragments of the meteorite were found following initial investigations. They had masses 242g and 61g, and were discovered some miles short of the calculated point of impact of the main mass - which is yet to be found. Two more small fragments were found nearby in 1940.

So the question remains, what stopped this from hitting us?

If a missle from earth hit it, then giant chunks would have rained down from the sky, the damage that it would have caused would be enormous.

On the other hand if it had hit Pennsylvania, then there would be a crater in the east coast even to this day.

Did extraterrestrials blow it up? that my theory

where did the rest of it go?

Huh...never heard of this before...my first reaction would usually be "Aliens!"...but there's just not enough info, the story is too vague...I guess if it's just as simple as a 496 tonne meteorite randomly exploding 12 miles from the Earths surface before impact...it could be Aliens...but there could also be other explanations...

This was a stony meteorite and would have likely broken into small pieces.
type Olivine-hypersthene chondrite

There is likely much more of it out there but i would look like regular rock so anyone other then a meteorite hunter would overlook them.

There are loads of reasons for a bit of space junk to loose cohesion on the way to the ground. The stress of entering the earths atmosphere, and all that heat... I mean come on man.
Another thing to consider, is that if there were any gasses inside the body of the object, then the heat from the friction of passing through the atmosphere could have raised the preasure in there, eventualy fracturing the thing, and splitting it into bitesize lumps.
Weirder crap has happened.

reply to post by TrueBrit


no i thought the same thing its the fact that they found less then 350 grams of a 496 ton meteorite. Not very often a meteorite of this size comes that close to the Earth. That would be like finding the blackbox of a 747 with maximum capacity crashed in pennsylvania

ANNED thanks for the info, but there were meteorologists on the site, they did a full investigation.

What no one has explained is why the meteroite exploded. I understand the burning up in the atmosphere but why this

The sound and light of the exploding meteor were initially mistaken for an explosion in the powder magazine at West Winfield

that is why it came to the conclusion of outside forces. What would cause the meteorite to explode?

With the source being Wikipedia it's impossible to rely too much on anything, I especially like how it's been calculated it was 496 tonne based upon small bits...

Nice story tho...

Very similar to the Tunguska event.. When a large stoney mass that large enters the atmosphere, there is a huge amount of compression heat causing massive pressure. THe object tend to burn up or explode before they reach the surface. In the Tunguska event, the meteor exploded knocking people off their feet and it scorched 800 sq miles knocking out trees, etc. There was virtually nothing found of that meteoroid.

There were about 1000 researchers looking at that one as well. They say these types of events typically result in air burst of the meteroids.

Double post, sorry...


[edit on 2-2-2010 by mapsurfer_]

Originally posted by Pajjikor
So the question remains, what stopped this from hitting us?

If a missle from earth hit it, then giant chunks would have rained down from the sky, the damage that it would have caused would be enormous.

On the other hand if it had hit Pennsylvania, then there would be a crater in the east coast even to this day.

Did extraterrestrials blow it up? that my theory

where did the rest of it go?

The meteor seen from Kecksburg PA on Dec 9 1965 exploded at an altitude of 32 km but like almost all meteors we didn't know it was coming until it hit our atmosphere.

However, there's an exception, a meteor we knew was coming and we tracked it and saw it explode at an altitude of 37km:

Meteorites Found in Africa From First Predicted Asteroid Hit

That meteor was the size of a pickup truck so it was quite a massive object, but the fragments found on the ground weighed only a few grams and looked like this:

[atsimg]http://files.abovetopsecret.com/images/member/df52760fdd30.jpg[/atsimg]
www.nasa.gov...

You seem to be surprised such an object would explode, but you shouldn't be, there is nothing unusual about such an explosion about an incoming meteor. If I understand correctly the forces that make a heated popcorn kernel pop are similar to the forces that can make an incoming meteor or comet explode, the heat makes volatile gases inside (such as water vapor etc) expand and such expansion creates internal pressure that causes an explosion.

The Tunguska event in 1907 was a very powerful explosion of an incoming comet or meteor that had an explosive force of about 10-15 megatons, perhaps 1000 times greater than the atomic bomb at Hiroshima. So they blow up naturally sometimes without any intervention from anybody.

As for where the rest of it went, well, just look at that picture of the remnants of the incoming meteor we tracked. Those fragments were hard enough to find in the barren desert. How much more difficult is it to find such fragments over an area covered with vegetation which will obscure the view of the fragments? Therein lies the answer to the question about where the rest of it is.

Regarding your theory that ET blew that or any of these up, well it's hard to comment on that theory without violating the T&C other than to say that there's just no basis in reality for such a theory.

[edit on 2-2-2010 by Arbitrageur]

reply to post by Pajjikor


Again I say , could just have been down to the components of which the meteorite was made. Could have been made from a compound that deals very well with the frozen depths of space, but is combustable at entry temperature!
I wonder what the chemical composition of the chunk they did find was?

reply to post by TrueBrit


I know i found lots of articles on the internet but the one that had the most data was wiki, so that the one i used. Dont like using it if i can avoid it but wiki makes sure there info is sourced, so it ok by me

Well there has been some good info posted here already by Arbitrageur and other posters, but I'd like to add a few words, since the physics of meteoroid impacts on our atmosphere is one area of science that has interested me for a while now.


Why do meteoroids not make it trough the atmosphere, and strike the ground with major force?

The answer is there are a number of factors...


1. Velocity

Most meteoroids Earth encounters are solar-system objects which are orbiting our Sun, and because of this when they hit our atmosphere they are traveling at a relative velocity of between 11-72 km/s. That is extremely fast!


2. Composition/Density/Structural Integrity

Because most meteoroids formed under low gravity, they are typically not very dense, and they are structurally quite weak. The vast majority are not much stronger that a sample of porous coal, and some can be as light and fluffy as cigarette ash.


3. Angle of entry

Too high an angle, and the transit into Earth's atmosphere is impossible to survive due to the forces and stresses involved. Too low of an entry angle and the meteoroid will skip off Earth's atmosphere like a rock skipping across a pond (that's just an analogy in the case of large objects which actually just "graze" the upper atmosphere). There is only a very narrow range of angles that will allow the stronger and slower objects to enter without being completely vaporised in the process.


4. Size/Mass

The bigger the rock, the more chance it has of surviving, and some of it making it down to the ground. However, being big can also make an object vulnerable to Earth's gravity, and as we saw with Shoemaker-Levy9, the object can start to break up due to the stress from gravity pulling on it.


To put these factors into some perspective, when a meteoroid slams into our atmosphere, it can be compared to taking a handful of slightly-moist good quality top soil, compacting it with your hands, and then throwing it as hard as you can into a deep body of water (our atmosphere).

What do you think happens to the "soil-ball"?

Will it hit the bottom and make a crater, or will it disintegrate in the top few inches of water?

Most meteoroids react in a similar kind of way, since to a meteoroid, our atmosphere is like hitting something hard, especially lower down where the air becomes very dense in relative terms. Even the quite sizable rocks, and many of the smaller iron metal meteoroids are slowed down drastically when they hit this part of the atmosphere.

In the vast majority of cases our atmosphere is a pretty effective shield against hypervelocity projectiles, even large ones.

Also, when something large disintegrates high up in the atmosphere, the remaining larger pieces will keep on going (until they slowed to free fall speed), but smaller pieces are completely vaporised, and this is usually most of the object. Even large objects are soon whittled away by the force of air atoms stripping off material (or being "ablated"), which gets more intense as the object breaks up and encounters denser air.

And that is why we would expect that most meteoroids, and even quite large asteroids are destroyed more or less completely, and usually only small remaining pieces are found.

The American Meteor Society have an excellent FAQ on the subject which covers all of the issues I mentioned.


[edit on 2-2-2010 by C.H.U.D.]

Hi CHUD my friend, starred your excellent post, it's nice to have a meteor expert here on ATS!

Originally posted by C.H.U.D.

3. Angle of entry

Too high an angle, and the transit into Earth's atmosphere is impossible to survive due to the forces and stresses involved. To low of an entry angle and the meteoroid will skip off Earth's atmosphere like a rock skipping across a pond. There is only a very narrow range of angles that will allow the stronger and slower objects to enter without being completely vaporised in the process.

That is quite true about only a narrow range of entry angles allowing an object to survive entry, it was a very critical mission parameter for the probe we sent into Jupiter that it had to fall within such a narrow band of entry angles.

However I should note that I posted a similar comment in another thread (searched for it but couldn't find it) about the shallow entry angle causing it to skip off the atmosphere and Jim Oberg corrected me that is a common misunderstanding/myth, popularized by an errant media report back in the day. What he told me actually fits better with my knowledge of physics, which is that if anything, rather than skipping off the atmosphere, the atmosphere provides drag attempting to slow it down, but the velocity of the object can be simply too great despite this drag and it just continues on a slightly altered trajectory back out into space.

I didn't find the thread where Oberg corrected me but I did find an excellent post by you in another thread with a diagram, which I'm sure you will recall but for the benefit of others to see the type of trajectory we are discussing I'll repost here:
www.abovetopsecret.com...

Originally posted by C.H.U.D.
This diagram should help you visualize what is going on:

So if you just extend that diagram, you can see that if the velocity is high enough and the atmospheric drag is low enough, a more or less straight line trajectory will cause the object on the left to just graze the Earth's atmosphere but miss the Earth, no skipping required.

So after Oberg told me that, I did a little research on it, and I found a paper by a scientist on atmospheric re-entry, and that scientist even used the phrase "skipping off the atmosphere" at a shallow entry angle. So I wondered if this is one of those myths that's so widely accepted out there that even some scientists think it's true?

After considering Oberg's comments and the research I did, my own conclusion is that he's probably right that meteors don't "skip off the Earth's atmosphere" at shallow entry angles which implies a force pushing them away from the Earth, to the contrary they experience atmospheric drag. The more correct phrase would be "graze the atmosphere" as your diagram shows on the left object.

I think this is probably true for most rocks and other objects entering the Earth's atmosphere, but a possible exception might be an aerodynamically designed space vehicle. To put this back in the context of your example of a stone skipping across the water, I know from personal stone-skipping experience that it helps to use stones with a particular shape to get them to skip, a flat stone skips well but a non-flat stone may not skip at all. I suspect this analogy may carry to the shape of objects entering the atmosphere also, and that a typical rock from space is probably not aerodynamically shaped enough to skip, but a space vehicle designed to be aerodynamic might be able to skip. I don't think I ever convinced Oberg of that latter point but that was the idea I got from reading the scientific paper I found talking about skipping off the atmosphere on atmospheric entry.

well thanks for the info, it explains all that i have questions to.

This is the reason for my postings here on ats. So much gets explained.

Pajjikor out

the skipping idea would work if it came in a a good trajectory but earths gravity would still pull down the meteor. its the same on a pond you cant get a rock to fly away from the water and keep going up. But maybe an spacecraft with a propulsion system could.

reply to post by Pajjikor


I think you have the idea. If the Earth were flat the pond analogy would be more apt, but of course it's not.

It's actually the curvature of the Earth (and curvature of the atmosphere) that makes it appear to fly back out into space after hitting the atmosphere without even changing direction, it can do so while traveling in a perfectly straight line, therefore, no propulsion, skipping or anything else is needed for it to appear to go "back into space". It's only inertia carrying it in a straight line and the curvature of the Earth provides the ILLUSION that it's moving back away from the Earth. An illustration should help:

[atsimg]http://files.abovetopsecret.com/images/member/fc284a96ed13.png[/atsimg]

Look at the altitude on the bottom, it appears to come closer to the Earth and then zoom back out into space. But look at the top to see what really happened, it was traveling in pretty much a straight line, except the atmospheric drag along with Earth's gravity actually changed its trajectory slightly TOWARD the Earth, NOT away from it as "skipping" would imply!


[edit on 2-2-2010 by Arbitrageur]

reply to post by Arbitrageur



Arbitrageur, good explanation friend and thanks for the kind words.

You are right, the "skipping off the atmosphere" explanation is only an analogy (at least in the case of large meteoroids). Sorry, I did not make that clear.

We usually call them "earthgrazers" or "grazers", as you quite rightly said. They are stunning meteors to behold by the way, and well worth the effort to try and see although they are not common. They can be seen early on in the night during the major annual meteor showers since Earth's rotation changes the angle of entry, from the fixed perspective of the observer over the course of the night.

I think the physics on grazing meteors may still be a little unclear. Shape as you said can play a part, and man made re-entries tend to be slow compared to some meteors. We also know that every action has an equal and opposite reaction in terms of force, and the combined impacts of billions of collisions with atmospheric gas molecules can generate significant force.

So, small meteoroids, which don't have so much momentum could potentially "skip", but something very large would have allot more momentum, and a much smaller "surface-area : mass" ratio (making harder to slow down), and so could not skip as easily.

I think Jim may well be right when it comes to artificial re-entry, since the objects are usually big and relatively slow, but for small and fast meteors I'm not so sure.

[edit on 2-2-2010 by C.H.U.D.]

Originally posted by C.H.U.D.
We usually call them "earthgrazers" or "grazers", as you quite rightly said. They are stunning meteors to behold by the way, and well worth the effort to try and see although they are not common.

I believe they are uncommon, and so much so that the idea of a meteor in horizontal flight seems to be a foreign concept to many people. That reminded me of this video of a pilot sighting an object in horizontal flight and says it can't be a meteor because it's impossible for a meteor to do that. However I suspect for a time that horizontal flight is exactly what grazers would do, though I would have guessed at a higher altitude. What do you think, do you think they saw a meteor?

Google Video Link

embedding seems a little finicky on that so try this if the embedded version doesn't work:
video.google.com...

Sure sounds like a meteor to me (The very first case on that video, Lufthansa 405).

[edit on 2-2-2010 by Arbitrageur]

Arbitrageur love the video, not quite sure what it is but there have been investigations into green fireball. sorta sounded like the same thing they were describing.

www.project1947.com...

Just finished it and gotta say that first clip both the pilots were pretty positive it was an aircraft.

Not sure what kind of compound would leave behind green smoke when burnt in the atmosphere. but that is the only way i could see it being a meteor.

Originally posted by Pajjikor
Just finished it and gotta say that first clip both the pilots were pretty positive it was an aircraft.

Not sure what kind of compound would leave behind green smoke when burnt in the atmosphere. but that is the only way i could see it being a meteor.

Glad you liked the video. I find it especially convincing when 2 pilots see the same thing and it's all documented like that.

I thought they said they thought it was an aircraft at first, but after it passed them they decided maybe it wasn't. L405 said he saw no navigation lights or any other signs it was an aircraft.

Regarding the green color, the FAQ that CHUD posted for us says something about green:

www.amsmeteors.org...

The dominant composition of a meteoroid can play an important part in the observed colors of a fireball, with certain elements displaying signature colors when vaporized. For example, sodium produces a bright yellow color, nickel shows as green, and magnesium as blue-white.

So if it was a meteor as I believe it was, it might have contained nickel.

When they asked L405 if it could have been a meteor, he was uncertain and said "I don't know". It was speedbird226 who said it wasn't a meteor because the flight path was level, but that's my whole point about grazers, they are rare but I think they could appear to have nearly level flight so perhaps he's wrong to rule a meteor out for that reason, especially one with nickel content which could survive into that low of an altitude I think. The other comments made by the controller that other pilots had reported a meteor kind of sealed my conclusion along with the bright light in front (nickel glowing white hot???) and a green smoke trail behind it (from the vaporizing nickel and other materials).